For playback of audio in headphones and hearing aids receivers are applied that convert an electric signal representing an audio stream into sound. A common type of receiver is the balanced armature type: an electro-acoustic transducer which converts energy from electrical energy to acoustical energy. Balanced armatures have limitations regarding the reproduction of sound due to e.g. nonlinearity of the flux field, saturation of the armature and mechanical compliance. The overall frequency response and bandwidth are affected by the design, dimension and construction of the balanced armature receiver. In particular, the balanced armature has typical resonant frequencies that influence frequency response. To address these limitations it is known to apply multiple receivers that are each designed to reproduce a specific portion of the sound frequency spectrum, such as e.g. tweeter, mid-range or woofer transducer assemblies reproducing high, mid and low frequency ranges respectively. As these frequency spectra may partially overlap, the joint frequency response of the receivers will be deficient likewise. To address this problem it is known to apply acoustic filters acoustically downstream. These are placed outside the spout of the receiver, but necessitate a complicated construction of the earphone itself to bring the sound of two receivers together into one acoustic channel to deliver the sound to the ear of a user. This means additional volumes affecting mainly the reproduction of higher frequencies. Moreover, installing such a receiver assembly in e.g. an ear phone product is more difficult and thus time consuming; which in turn increase costs of manufacture. In order to reduce the amount of space taken up by a multiple receiver assembly, dual receiver assemblies have been developed wherein two transducer assemblies are combined in a single housing with a single spout; usually a combination of a woofer and a tweeter or a woofer and a mid-range receiver. To further reduce the amount of space taken up by a dual receiver assembly, in U.S. 2009/0060245 it is disclosed to apply a constriction plate with a generally circular shaped aperture located inside the spout, instead of a complex construction outside of the spout. The aperture functions as an acoustic low pas filter and is applied to the sound outlet port of a woofer transducer assembly. However, the filter response of the circular aperture in the constriction plate is strongly non-linear resulting in undesirably high time harmonic distortions.
It is an object of the present invention to provide a receiver assembly that overcomes the drawbacks mentioned above.